Spitzer Space Telescope - General Observer Proposal #12096
A Spitzer Transit of the Most Inflated Planet Known, Around an Extremely Bright
Sub-giant Star
Principal Investigator: Thomas Beatty
Institution: Pennsylvania State University
Technical Contact: Thomas Beatty, Pennsylvania State University
Co-Investigators:
Karen Collins, Vanderbilt University
Knicole Colon, Kepler/K2 Guest Observer Office
David James, CTIO
Laura Kriedberg, University of Chicago
Joshua Pepper, Lehigh University
Joseph Rodriguez, Vanderbilt University
Robert Siverd, LCOGT
Keivan Stassun, Vanderbilt University
Daniel Stevens, Ohio State University
Science Category: extrasolar planets
Observing Modes: IRAC Post-Cryo Mapping
Hours Approved: 15.5
Priority: 1
Abstract:
KELT-11b is a newly discovered transiting Saturn-mass planet (Mp~0.22MJ) that
promises to become a unique benchmark. KELT-11b orbits HD 93396,the second
brightest star in the near-IR (K=6.122) and the third brightest star in the
optical (V=8.04) to host a transiting giant planet. This makes KELT-11
comparable to the well-studied benchmarks HD 189733 and HD 209458. But unlike
these other bright systems, KELT-11b's host star is a sub-giant, with
log(g)~3.7. Thus KELT-11b is the first transiting giant planet known around a
sub-giant star bright enough for precise follow-up observations. Furthermore,
KELT-11b is the most inflated planet known, with the lowest surface gravity
(log[g]~2.5) of any transiting planet. This makes it an exciting target for
atmospheric characterization and studying the effect of post main-sequence
evolution of a host star on a hot Jupiter. But to correctly interpret any
follow-up observations, we will first need to measure accurate stellar and
planetary parameters for the system via a precise transit observation.
Unfortunately, this is effectively impossible to do from the ground. Spitzer's
ability to provide high precision continuous photometry provides the only
current way in which we may precisely observe a complete transit of KELT-11b.
We therefore propose for 15.5 hours, to observe a single transit KELT-11b at
3.6um. This would reduce the uncertainties on the transit depth and stellar
density by at least a factor of twenty, and will improve the model-derived
stellar mass by at least a factor of ten, compared to ground-based observations.
This will serve two goals. First, it will be a valuable legacy to the community,
by providing a precise set of system parameters that will enable future
observation and interpretation of this unique, bright, system. Second, an
observation of a transit will allow us to strongly constrain the mass of
KELT-11, and thus help resolve the disagreement over the true masses of the
"retired A stars" radial-velocity sample.